If somebody wants to make substantial modifications on their home, they're going to need new permits. 'Those are the homes that are going to require flood insurance, if somebody wants to buy a home within the floodplain. 'That's going to put a lot of new homes in the floodplain,' Rahman said. Under the new maps, the areas subject to those rules will expand. MORE ON FLOOD MAPS: Post Harvey, 1 in 8 Houston homes permitted are in floodplains, as developers reshape flood maps Under the post-Harvey regulations, buildings now have to be constructed two feet above the 500-year storm level, and that applies to properties in the 500-year floodplain, as well. Under the old rules, development in the 100-year floodplain had to be built one foot above the projected water level in a 100-year storm. In response to Harvey, Harris County and the city of Houston made significant changes to building regulations, passing rigorous elevation rules. Having updated maps with more accurate boundaries also impacts the community as a whole - the maps guide planning and determine where development can occur. What the new maps mean for HoustoniansįEMA's floodplain maps determine whether property owners are required to buy flood insurance and affect the cost of that coverage. On the new maps, Harris County's 100-year floodplain will increase from around 150,000 acres to 200,000 acres, according to County Engineer Milton Rahman. Most floodplains in Harris County will increase substantially because the new rainfall estimates mean the region will be preparing for bigger storms with around 30 percent more rain. MORE ON FLOODING: Why climate change and urban sprawl could make flooding worse in Harris County The new maps also will reflect updated rainfall estimates from the National Oceanic and Atmospheric Administration that better depict the reality that storms have intensified in recent decades, data that had not been updated since the 1960s.Ĭommunities across the United States are going through the process of updating their floodplain maps to align with NOAA's higher rainfall estimates.

The new floodplain maps developed by the Harris County Flood Control District will be FEMA's first maps to depict urban flooding. Until now, the maps have not shown the risk of urban flooding - when intense rainfall overwhelms stormwater systems regardless of how close it is to a bayou or other channel. That is not the only type of flooding that affects Harris County. IN-DEPTH: New Harris County flood maps will be first in US to show more accurate risks for homes, businessesįEMA's existing maps show communities their risk of fluvial, or river flooding - that's when a bayou, creek or lake overflows its banks and floods nearby structures. Now, on the new maps, most of Harris County's floodplains will expand, reflecting a major effort to capture a more comprehensive understanding of flood risk. Located outside FEMA's mapped floodplains, they did not realize they were at risk. In past storms like the Memorial Day flood, the Tax Day flood and Hurricane Harvey, many people who flooded were caught by surprise.

Houston flood zone map